1. Field of the Invention
The present invention relates to a rotating electrical machine and a manufacturing method thereof.
2. Description of the Related Art
In recent years, operating rotating electrical machines at variable speeds using an inverter device has become widespread, from the perspective of energy conservation. However, it has been reported that in the event of driving a rotating electrical machine using an inverter device, voltage higher than when driving with conventional commercial frequency power is generated between coils making up the stator coils of the rotating electrical machine, due to steep surge voltage occurring when operating the inverter device (e.g., see Institute of Electrical Engineers of Japan Technical Report vol. 739, pp 14-20). Conventionally, this problem has been handled by reinforcing insulation or improving voltage distribution between coils with regard to the surge voltage.
Of these methods, reinforcing insulation is carried out by reducing the number of winds of the stator coils where the surge voltage from the inverter is applied, and making the insulating covering thicker (e.g., see Institute of Electrical Engineers of Japan Rotating Machine Study Team Material RM-00-95). However, this method changes the machine output properties of the rotating electric machine, and accordingly is limited in its extent.
With the latter method of improving the voltage distribution between coils, study has been carried out regarding high-voltage and steep surge voltage such as lightning impulses and on/off surges of vacuum breakers, in devices such as high-voltage motors, high-voltage generators, and other like high-voltage rotating machines, high-voltage transformers, reactors, and other like high-voltage stationary induction devices, even before surge voltage of inverter devices became problematic. For example, a method has been proposed to analyze voltage distribution between coils by approximating electromagnetic coils with an equivalency circuit formed with inter-coil capacitance and to-ground capacitance of various portions of the coils, and calculating the voltage distribution with regard to unit step voltage (e.g., see Masayuki Ieda “Gendai Koden'atsu Kogaku (Modern High-voltage Engineering)” pp 91-93, published by Ohmsha).
Also, A proposal has been made to design the to-ground capacitance of each the parts of the coils smaller in comparison with the distributed capacitance between coils, thereby reducing the voltage distribution between coils. Further, with regard to high-voltage rotating electrical machines, a proposal has been made for a method to alleviate inter-coil voltage balance by connecting capacitors externally from the coils, for adjusting capacitance distribution between coils (e.g., see JP-A-50-301).
Further, a three-phase distributed winding arrangement is know for conventional rotating electrical machines, as described in JP-A-2002-51489, for example.